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The bacterium known to humans as Yersinia pestis has terrorized and inflicted innumerable miseries upon humans over the course of centuries. According to an estimate, it has killed around 200 million people and has been responsible for the plagues in the 6^th and the 14^th centuries. However, this was not the case earlier and this germ was not always this dangerous and this highly contagious. At that time the pandemic was caused due to the Yersinia Pestis bacteria transmitted through flea bites. The infection that is known today is something that has mutated from an earlier ancestor of the bacteria which caused a respiratory ailment called the pneumonic plague. Later on, after the mutation, came the bubonic plague. A study suggests that even today the Black Death disease exists but in a different, mutated form. The bacterium strain present today has been evolved from a species known as Yersinia pseudotuberculosis. In the study the scientists have said that the new research might explain how Y.pestis went on from causing only localized outbreaks to be the main cause of the pandemic spread in the 6^thcentury’s Justinian Plague and the 14^th century’s Black Death.

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The researchers performed mice examination that frequently retraced to the familiar modification tendency among the germs. The research team was led by Wydham Lathem, an assistant professor in microbiology-immunology at the Northwestern University’s Feinberg School of Medicine in Chicago.

Lathem suggested that the bacteria’s acquisition of the gene PLA enhanced its ability to cause infection in the lungs and was all that this ancestral strain needed to cause a contagious and fatal lung infection. It was also found that the plague bacteria with the amino acid change had the ability to cause the invasive infection associated with bubonic plague today. The researchers found that it contained a gene protein PLA protease which is not present in the older species of the microorganism.

Earlier the studies showed that this amino acid mutation is responsible for a slight change in the activity of PLA, but it was not fully proved and was done only in the labs in the test tubes. The acquiring of PLA by Yersinia allowed it to flow through the bloodstreams of the infected quite easily and spread the infection all around the body of the patient. This bacterium can be transmitted from one person to another through respiratory droplets. These droplets can only infect those who have been in face-to-face contact with the infected. The CDC indicated that people can get affected by this bacterium if they have been bitten by the fleas carried on rodents.